1. Field of the Art
The present invention relates to a serial printer which is capable of printing on a multiple-copy or multiple-sheet recording medium consisting of a plurality of sheets superposed over each other, and more particularly to a device for preventing a print head of the printer from interfering with temporary binder or fastener means provided along opposite lateral edges of the recording medium.
2. Related Art Statement
In the art of printing on a recording medium of the type indicated above, the recording medium in the form of a stack of paper sheets has feed perforations formed in spaced-spart relation along the side or lateral edges of the medium, so that the recording medium may be fed through engagement of the feed perforations with sprockets formed on sprocket wheels or belts of a printer. Where such a multiple-sheet recording medium consists of five or six sheets of paper or more stacked on each other, the uppermost and lowermost sheets of the stack tend to be displaced relative to the inner sheets. To avoid this displacement, the component paper sheets of the stack are temporarily bound with suitable temporary binding or fastening means which are formed between the feed perforations, for example, by so-called "paper Hotchkiss" punches, so as to create narrow strips that are partially punched-out portions of the sheets and connected at their one side to the sheets. The punched-out portions serve to bind or fasten the sheets together. But, the narrow strips of the temporary binding means partially connected to the multiple-sheet medium may be upraised above the surface of the medium when it is fed through a paper guide in the printer, thereby giving the medium local upraised areas which may interfere with a print head. In this event, the medium may be jammed and damaged between the print head and a platen.
When a line of characters is printed from left to right, for example, within a preset range, the print head is moved a certain distance beyond the rightmost character position, before a carriage carrying the print head is decelerated and finally stopped. This distance of movement is also required for accelerating the carriage to a normal printing speed before the print head starts printing a first character of each line, which is either the rightmost or the leftmost character of the line. Therefore, when the rightmost or leftmost character is located near the corresponding edge of the medium, i.e., near the temporary binding portions, the print head may be located between the upper and lower temporary binding portions after the print head has printed the last character of a line, or before the print head starts printing the first character of a line, irrespective of whether that line is printed in a rightward direction or in a leftward direction. If the recording medium is advanced to the next line in the above-indicated condition, the print head may interfere with the lower temporary binding portion.
To prevent an interference of the print head with temporary binding portions, and consequent damages to the medium, it is proposed to move the print head in a direction away from the binding portions at the end of printing of each line, and before the medium is advanced to the next line. An alternative proposal to solve the inconveniences in question is to use a sensor for detecting the temporary binding portions so as to move the carriage and the print head away from the detected binding portions if the print head is located within a margin area which overlaps the temporary binding portions.